Support narrowing a cpu profile to a given time window

sdk/lib/developer/timeline.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.developer;
 
 typedef dynamic TimelineSyncFunction();
 typedef Future TimelineAsyncFunction();
 
 /// Add to the timeline.
@@ skipping 50 matching lines @@
                           TimelineSyncFunction function,
                           {Map arguments}) {
     startSync(name, arguments: arguments);
     try {
       return function();
     } finally {
       finishSync();
     }
   }
 
+  /// The current time stamp from the clock used by the timeline. Units are
+  /// microseconds.
+  static int get now => _getTraceClock();
   static final List<_SyncBlock> _stack = new List<_SyncBlock>();
   static final int _isolateId = _getIsolateNum();
   static final String _isolateIdString = _isolateId.toString();
 }
 
 /// An asynchronous task on the timeline. An asynchronous task can have many
 /// (nested) synchronous operations. Synchronous operations can live longer than
 /// the current isolate event. To pass a [TimelineTask] to another isolate,
 /// you must first call [pass] to get the task id and then construct a new
 /// [TimelineTask] in the other isolate.
@@ skipping 176 matching lines @@
                                    int end,
                                    String category,
                                    String name,
                                    String argumentsAsJson);
 
 /// Reports an instant event.
 external void _reportInstantEvent(int start,
                                   String category,
                                   String name,
                                   String argumentsAsJson);